The invention refers to an apparatus for pneumatically conveying bulk material, and in particular to an apparatus including a conveyor line for transporting the bulk material and a secondary line which guides a clean gas and is connected via spaced valves with the conveyor line for introducing clean gas into the conveyor line as soon as the pressure differential as measured between adjacent measuring elements which are spaced along the conveyor line exceeds a predetermined value.
An apparatus of this kind is known from the German publication DE-OS No. 34 35 907. Each of the measuring elements is connected to the secondary line and contains a pressure-reducing valve which is controlled by a diaphragm acted upon by the pressure prevailing in the conveyor line. The pressure-reducing valve supplies a clean-air receiver in which the same pressure prevails as in the conveyor line and which is connected in the area of the next succeeding measuring element in downstream direction with the conveyor line via a line and a check valve.
In case a clogging is forming within the conveyor line, the pressure difference between the clean-air receiver of the next succeeding measuring element in upstream direction and the conveyor line in the area of the associated check valve exceeds the closing force of its spring so that the check valve opens and allows introduction of additional clean air into the conveyor line.
In case of need, such an apparatus allows a simultaneous supply of clean air into the conveyor line at several points thereof. However, the measuring elements which include complicated specially designed valves must be spaced from each other at distances which correspond at a maximum to the length of a clogged area and thus must be provided in great numbers in order to ensure a dissolution of a clogged area. In addition, only a limited overpressure according to the pressure difference between adjacent measuring elements is available for dissolving the clogged area. A further drawback resides in the fact that in case a check valve fails to operate, bulk material may penetrate the associated measuring element thus impairing functioning thereof.